The present invention relates to a method for determining parameters for the viscosity and/or temperature of a brake fluid of a vehicle.
It is known that the viscosity of a brake fluid or hydraulic fluid is greatly responsive to temperatures. High viscosity at low fluid temperatures, i.e., at a low temperature below −10 degrees C., for example, in the starting period of an automotive vehicle impairs the controllability of the brake pressure of a controlled hydraulic brake system. It is problematic when the brake fluid is used in a system having a driving stability control function, which operates without being influenced by the driver, and fluid must flow especially quickly from the brake fluid reservoir to a wheel brake. With temperatures dropping, the viscosity of the brake fluid rises at a high rate. At very low temperatures, the result is that the brake fluid cannot flow at a sufficiently quick rate and, in addition, the loss in pressure in the pipe line increases with rising viscosity. These obstacles cause a slower brake intervention. In driving stability control, however, there is the general demand of effecting a quick brake intervention. To solve this problem, devices have already been proposed which provide an auxiliary pressure source or a precharging pump. Because this entails considerable extra cost, the use of these devices is increasingly avoided.
In view of the above, an object of the present invention is to ensure, with little effort, the functioning of a hydraulic vehicle brake system with all its partial functions, such as anti-lock function, traction slip function, and driving stability function, at any temperatures, even when exposed to very low outside temperatures.